It is well known that when different plant lines are cross-pollinated one can achieve in the offspring a highly desirable heterosis or hybrid vigor which advantageously provides increased yields of the desired crop.
Representative crops which have been successfully hybridized in the past include sugar beets, corn (See U.S. Pat. No. 3,753,663 to Jones), sorghum, alfalfa (See U.S. Pat. No. 3,570,181 to Davis), wheat, sunflowers, cotton, rice (See U.S. Pat. No. 4,305,225 to Yuan), cucumbers, onions, carrots, and tomatoes.
Soybeans (i.e., seeds of Glycine max plants) are recognized to be an important crop in many parts of the world. For instance, approximately 65 to 75 million acres of soybeans are planted annually in the United States which establishes this to be the largest seed crop presently grown in the United States. However, in spite of research by many skilled plant scientists over the past 50+ years, soybeans represent the last major seed crop which is not being grown by the farmer in a hybridized form. Accordingly, the farmer heretofore has not had available seed capable of growing hybrid soybean plants which exhibit a vigor which is attributable to the crossing of two diverse parent lines.
As reported in Modern Soybean Production, by Walter O. Scott and Samuel R. Aldrich, published by The Farm Quarterly, Cincinnati, Ohio 45210 in 1970:
"The secret of producing hybrid soybean seed on a commercial scale is yet to be discovered." PA1 "Hybrid soybeans can also become a possibility if a technique is developed to sort out hybrid seeds from selfed seeds." PA1 "If hybrid soybeans become a reality, plant breeders must pay strict attention to floral characteristics and include compatibility of these factors in their breeding programs." PA1 "The announcement in 1974 (Bradner) of a patent on hybrid soybean seed production initially created some excitement. We should consider the possibility of hybrid soybeans. There are three major requirements for hybrid soybean production: (1) a male sterile, female fertile mutant(s) (either genetic or cytoplasmic-genetic); (2) a high level of pollen transfer from male fertile to male sterile (female parent) plants; and (3) sufficient hybrid vigor to warrant production. With the present genetic male steriles (ms.sub.1 and ms.sub.2), only 50% of the plants in a female production row will be male sterile. This is the highest percentage of male sterile plants that can be expected." PA1 "The successful utilization of sterility mechanisms in producing commercial hybrids of mostly cross-pollinated crops such as corn, sorghum, and onions is well known. In these crops cytoplasmic male sterility coupled with nuclear genes which restore fertility has contributed greatly to decreased cost of seed production. Although not essential to seed production in corn, the sterility mechanism was adopted universally as a means of reducing costs. The success of hybrid corn, sorghum, and onions has not gone unnoticed by plant breeders working with other crops, and considerable effort has been expended in attempts to exploit hybrid vigor in almost every species of economic importance. PA1 Soybeans are an obligate self-fertilizer and pollination takes place before the female parts of the flower are exposed to vectors which carry foreign pollen. Therefore, there is no alternative to a male sterility mechanism in achieving natural crossing in the species. But if we are concerned with hybrid seed production only, the availability of a sterility mechanism is of little use unless hybrid vigor is great enough to offset cost of production. The known male sterility mechanism in soybeans is determined by male-sterile plants can only be obtained from a "maintainer" line which segregates for fertility and sterility. The male fertile plants must be removed at flowering to obtain only cross seed." PA1 (a) a male sterile female parent wherein the male sterility was attributable to the combination of an atypical Cms cytoplasm and two pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2, and PA1 (b) a male fertile male parent which possessed at least one pair of dominant genes selected from the group consisting of R.sub.1 R.sub.1 and R.sub.2 R.sub.2 which was capable of restoring male fertility to the off-spring, and PA1 (a) a male sterile female parent wherein the male sterility was attributable to the combination of an atypical Cms cytoplasm and two pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2, and PA1 (b) a male fertile male parent which possessed at least one pair of dominant genes selected from the group consisting of R.sub.1 R.sub.1 and R.sub.2 R.sub.2 which was capable of restoring male fertility to the off-spring, and
As indicated by B. B. Singh in "High Frequency of Natural Cross Pollination in a Mutant Strain of Soybean", Current Science, Vol. 41, No. 25, p. 832-833, 833(1972):
As indicated in "Bee Pollination of Soybeans" by Eric H. Erickson, Proceedings of the Sixth Soybean Seed Research Conference 1976, p. 46-49, 49:
As indicated in "Cytogenetics in Soybean Improvement" by Reid R. Palmer, Proceedings of Sixth Soybean Seed Research Conference 1976, p. 56-66, 60:
Finally, it is written by Charles A. Brim in "Implications of Male-Sterility in Soybeans", Proceedings of the Sixth Soybean Seed Research Conference 1976, p. 67-74, 67:
As indicated, soybean plants (i.e., Glycine max plants) are recognized to be naturally self-pollinated plants which while being capable of undergoing cross-pollination rarely do so. Insects are reported by some researchers to carry pollen from one soybean plant to another and it generally is estimated that less than one percent of soybean seed formed in an open planting can be traced to cross-pollination, i.e., less than 1 percent of the soybean seed formed in an open planting is capable of producing F.sub.1 hybrid soybean plants (i.e., hybrid soybean plants of the first filial generation). See the articles by Elbert R. Jaycox entitled "Ecological Relationships between Honey Bees and Soybeans" appearing in the American Bee Journal, Vol. 110(8): 306-307 (August 1970), Vol. 110(9): 343-345 (September 1970) and Vol. 110(10): 383-385, (October 1970).
The relatively low proportion of cross-pollination commonly observed in soybean plants when grown in nature can be traced to the characteristic floral configuration exhibited by soybean plants. The pistillate (female) and staminate (male) elements of soybean flowers are normally present on the same plant and are located within perfect flowers which contain both elements in a juxtaposed relationship. The opening of the individual soybean flowers (florets) is believed to be triggered by the temperature and the length of time the plant is exposed to light. However, the anthers and stigma continue to be tightly enclosed within petals (i.e., the portion of the flower known as the keel petals). When dihiscence of anther tissue occurs and pollen is shed from the anthers, it tends immediately to contact the stigma in the same floret and is retained there by the keel petals. A seed pod ultimately is formed from this fertilization assuming that the pollen does not abort. Accordingly, soybean plants normally are cleistogamous since the flowers are self-fertilized while still in the unopened state.
Cytoplasmic male sterility has never been observed in soybean plants in the past in spite of extensive plant breeding and prolonged searching within huge populations of soybean plants of many different varieties. However, some researchers have reported the existence of partial or complete male sterility in soybean plants which can be attributed to other factors such as chromosome abnormalities, viral conditions, genetic transmission attributable solely to nuclear genes, etc. None of the above types of male sterility heretofore observed has provided a real basis for the production of hybrid soybeans on a commercial scale. For instance, if the male sterility is attributable to nuclear genes the sterility can be perpetuated only through a line which segreates as for fertility and sterility. Accordingly, male fertile soybean plants are inevitably produced along with the male sterile soybean plants in the total absence of a meaningful control whereby only male sterile soybean plants are formed.
Representative publications which discuss the existence of some degree of sterility in soybean plants which is not attributable to the cytoplasm are as follows:
(1) "A Partially Male Sterile Strain of Soybeans", by C. E. Caviness, H. J. Walters, and D. L. Johnson, Crop Science, Vol. 10, p. 107-108, (Jan.-Feb. 1970), PA0 (2) "Inheritance of a Male-Sterile Character in Soybeans", C. A. Brim and M. F. Young, Crop Science, Vol. 11, p. 564-566, (July-Aug. 1971), PA0 (3) "Influence of Temperature on a Partially Male-Sterile Soybean Strain", by C. E. Caviness and B. L. Fagala, Crop Science, Vol. 13, p. 503-504 (Sept.-Oct. 1973), PA0 (4) "Implications of Male-Sterility in Soybeans", by A. Brim, Proceedings of the Sixth Soybean Seed Research Conference 1976, p. 67-71, PA0 (5) "Technology of Hybrid Soybeans", by W. H. Davis, Proceedings of the Sixth Soybean Seed Research Conference 1976, p. 72-74, PA0 (6) "A New Male-Sterile Strain in Wabash Soybeans", by H. K. Chaudhari and W. H. Davis, J. of Heredity, Vol. 68, p. 266-267 (1977), PA0 (7) "Pollen Production in Soybeans With Respect to Genotype, Environment, and Stamen Position", by R. G. Palmer, M. C. Albertson, and H. Heer, Euphytica, Vol. 27, p. 427-433 (1978), PA0 (8) "Genetics and Cytology of the ms.sub.3 Male-Sterile Soybean", by R. G. Palmer, C. W. Johns, and P. S. Muir, J. of Heredity, Vol. 71, p. 343-348 (1980), PA0 (9) "Pollination of Male-Sterile Soybeans in Caged Plots", by P. D. Koelling, W. J. Kenworthy, and D. M. Caron, Crop Science, Vol. 21, p. 559-561 (July-Aug. 1981), PA0 (10) "Variable Development in Anthers of Partially Male-Sterile Soybeans", by D. M. Stelly and R. G. Palmer, J. of Heredity, Vol. 73, p. 101-108 (1982), and PA0 (11) "Genetics and Cytology of the ms.sub.4 Male-Sterile Soybean", by X. Delanney and R. G. Palmer, J. of Heredity, Vol. 73, p. 219-223 (1982). PA0 (a) growing a substantially uniform population of male sterile soybean plants wherein the male sterility is attributable to the combination of an atypical Cms cytoplasm and two distinct pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2 in pollinating proximity to a substantially uniform population of male fertile soybean plants which possess at least one pair of dominant genes selected from the group consisting of R.sub.1 R.sub.1 and R.sub.2 R.sub.2 and which when crossed with the male sterile soybean plants enable the formation of seeds on the male sterile soybean plants which are capable of growing male fertile F.sub.1 hydrid soybean plants, PA0 (b) crossing the male sterile soybean plants and the male fertile soybean plants (preferably with the aid of pollen carrying insects) whereby seeds are formed on said male sterile soybean plants, and PA0 (c) selectively recovering seeds which have formed on the male sterile soybean plants. PA0 (a) growing in a planting area a substantially random population of (i) male sterile soybean plants wherein the male sterility is attributable to the combination of an atypical Cms cytoplasm and two distinct pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2, and (ii) male fertile soybean plants which possess at least one pair of dominant genes selected from the group consisting of R.sub.1 R.sub.1 and R.sub.2 R.sub.2 and which when crossed with the male sterile soybean plants enable the formation of seeds on the male sterile soybean plants which are capable of growing male fertile F.sub.1 hybrid soybean plants, PA0 (b) pollinating the substantially random population of soybean plants (preferably with the aid of pollen carrying insects) whereby seeds are formed on the male sterile plants which are capable of growing male fertile F.sub.1 hybrid soybean plants and seeds are formed on the male fertile soybean plants as a result of self-pollination, and PA0 (c) recovering seeds which have formed on the substantially random population of soybean plants growing in the planting area. PA0 (a) growing a substantially uniform population of male sterile soybean plants wherein the male sterility is attributable to the combination of an atypical Cms cytoplasm and two distinct pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2 in pollinating proximity to a substantially uniform population of male fertile soybean plants which possess an N cytoplasm and two distinct pairs of recessive genes r.sub.1 r.sub.1 and r.sub.2 r.sub.2, PA0 (b) crossing the male sterile soybean plants and the male fertile soybean plants (preferably with the aid of pollen carrying insects) whereby seeds are formed on the male sterile soybean plants which upon growth yield additional male sterile soybean plants, and PA0 (c) selectively recovering seeds which have formed on the substantially uniform population of male sterile soybean plants. PA0 (1) male fertile F.sub.1 hybrid soybean plants which were the result of cross-pollination between: PA0 (2) male fertile soybean plants which were the result of the self-pollination of the male fertile male parent (b) identified with respect to binary component (1). PA0 (1) male fertile F.sub.1 hybrid soybean plants which were the result of cross-pollination between: PA0 (2) male fertile soybean plants which were the result of the self-pollination of the male fertile parent (b) identified with respect to the binary component (1).
Unpublished data (to be published in a monograph in the future) recently provided by Reid G. Palmer indicates that the following genes were known in the past to cause sterility in soybeans:
______________________________________ Gene Identification Phenotype Source Strain ______________________________________ st2 Asynaptic sterile T241 st3 Asynaptic sterile T242 st4 Desynaptic sterile T258 st5 Desynaptic sterile T272 fs1 Structural sterile T269 fs2 Structural sterile T269 ft Structural sterile Gamma ray induced mutant msp Partial male sterile T271 ms1 Male sterile T260, T266, T267, T268 ms2 Male sterile T259 ms3 Male sterile T273 ms4 Male sterile T274 ms5 Male sterile T277 ______________________________________
U.S. Pat. Nos. 3,903,645 and 4,077,157 to N. R. Bradner concern still different approaches to the production of hybrid soybeans In the former patent the hybrid seed is formed on a seed parent having an atypical exposed floral stigma. In each instance, the pollination is not fully controlled with both cross-pollination and self-pollination taking place. The resulting seeds are subsequently separated on the basis of size. The processes of these patents are yet to become a commercial reality.
It is an object of the present invention to provide an improved procedure for forming F.sub.1 hybrid soybean plants which is capable of being readily implemented on a commercial scale.
It is an object of the present invention to provide an improved procedure for forming F.sub.1 hybrid soybean plants wherein the requisite cross-pollination needed to produce the hybrid is precisely controlled thereby eliminating the possibility of unwanted self-pollination.
It is an object of the present invention to provide an improved procedure for forming F.sub.1 hybrid soybean plants wherein the seed parent is the result of a controlled plant breeding program wherein previously widely dispersed factors are combined which have been found to be necessary if the requisite male sterility is to be exhibited.
It is an object of the present invention to provide an improved procedure for forming F.sub.1 hybrid soybean plants wherein the seed parent is the result of a controlled plant breeding program wherein factors found necessary to express complete sterility are combined using well known techniques and readily available commercial soybean varieties.
It is an object of the present invention to provide soybean plants and seeds capable of forming the same which are fully male sterile as a result of the requisite combination of cytoplasmic and genetic factors found to be necessary to express this important characteristic.
It is a further object of the present invention to provide vigorous F.sub.1 hybrid soybean plants wherein said vigor is attributable to heterosis and seeds capable of forming the same which are derived from a fully male sterile seed parent having the requisite combination of cytoplasmic and genetic factors found to be necessary to express this important characteristic.
It is an additional object of the present invention to provide novel agronomic technology which will increase soybean yields via heterosis and the income of farmers who choose to apply such technology.
These and other objects of the claimed invention, as well as its scope, nature, and utilization will be apparent to those skilled in plant technology from the following detailed description and appended claims.